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Based on this information, I suspect the singer had Stage 3 HPV+ squamous cell carcinoma of the tongue that was treated primarily by radiation and chemotherapy. If any residual cancer was detected after this treatment, the rest would have been surgically excised.
For those who follow celebrity news, Michael Douglas suffered the same type of tongue cancer due to HPV and underwent the same type of treatment.
HPV has become one of the leading causes of oral cancer in those under 50... even more of a risk factor than smoking and alcohol. HPV is suspected to be transmitted through oral sexual contact.
Iron Maiden Singer Bruce Dickinson Says He Got Tongue Cancer from a Sexually Transmitted Virus. People.com 9/4/15